1. Field of the Invention
The present invention relates to an elastic hinge for connecting a side arm to a front part of a pair of spectacles. When their arms are moved from their "open" position corresponding to wearing the spectacles, to their "closed" storage position, such elastic hinges produce a snapping effect; they moreover allow the arms to be moved apart elastically beyond their "open" position. Such hinges are greatly appreciated by the public, in particular due to the fact that they enable the spectacle frame, even if used extensively, to be held with the proper configuration, and also because the side arms bear against the temples with a reasonable pressure.
2. Description of the Prior Art
Generally speaking, an elastic hinge is made up on the one hand of a front hinge element (or charnier) solidly secured in the side lug of the front part and, on the other hand, a side hinge element connected by an elastic biasing mechanism to the end of the side arm, with a pin connecting the hinge elements.
A first known type of biasing mechanism, called the "slide" type, comprises a sliding part which is slidably mounted inside a casing arranged at (or fixed to) the end of the side arm, the protruding end of the sliding part carrying a male or female charnier. The other side charnier is cam-shaped and bears against the housing's mouth. In the sliding part is a longitudinal space housing a spring whose end bears against an abutment such as a shaft, pin or screw that passes through and is fixed with the casing. When the side arm is pivoted, the front charnier pushes back the casing, which causes the sliding piece to move out elastically. This type of elastic hinge is, for example, described in EP 0 091 573, FR 2 258 642, FR 1 511 263, EP 0 426 947 and FR 2 702 573.
In a second known type of biasing mechanism, called the "rod" type, the side charnier, usually of the male type, is arranged at the protruding end of central rod slidably mounted inside a housing provided in or attached to the end of the side arm. The female front charnier is cam-shaped and bears against the housing's mouth. A spring located around this central rod bears on one side against a thick end part of the rod and, on the other side, against a pin passing through this housing or against a restriction-forming abutment engaging into the inner face of the housing. When the side arm is pivoted, the front charnier pushes back this housing which causes the sliding piece to move out elastically. This type of elastic hinge is, for example, described in EP 0 340 161, FR 2 609 816, or FR 2 664 990.
A third type of elastic hinge, known as the "sheath" type, described in FR 2 517 080, comprises a male charnier provided directly at the end of the side arm and connected by a screw to a female charnier integral with the frame's front part. A sheath is slidably mounted on the side arm in the proximity of the male charnier. The front face of this sheath is pushed against the cam-shaped female charnier by a spring that is also arranged concentric to the side arm and bears by its rear against an abutment, such as a crimped ring or an adhesively-bonded sleeve, integral with this side arm. When the side arm is pivoted, the front charnier pushes back the sheath by compressing the spring.
These hinges have a drawback in their connecting pin, usually formed by a screw whose threads engage in a bore in one of two eyelets making up the female hinge: if the screw is too tight it is difficult to open the side arm; if it is loose, it can unscrew and become lost.
In this regard, from U.S. Pat. No. 1,504,212, FR 1 126 049, DE 34 04 511 and DE 44 21 309 hinges are known wherein the connection pin is an integral part of the male charnier, protruding perpendicularly from both sides.
The female charnier of the first document consists of a cylinder with an inverted T or L shaped slot leading into the upper edge. During assembly, the pin is inserted into the cylinder and the side arm is passed into the vertical part of the slot to then be pivoted in the horizontal part. To prevent dismantling of the hinge, a nut is screwed in a threaded part at the pin's lower end emerging under the cylinder. Unfortunately, this nut is as unreliable as traditional screws.
The pin of the male charnier of the second document has two flats, and the two eyelets of the female charnier each have a slot aligned with one another with a spacing corresponding to the thickness separating the two flats. These flats are angularly positioned so that they can only pass through the slots in one angular position, outside the angular play corresponding to the open or closed arm. As a result, to assemble and snap together the hinge, the side arm must be temporarily bended. This type of hinge is principally intended to be manufactured from molded plastic material, which necessitates making it of large dimensions.
In the fourth document's hinge, the two eyelets of the female charnier each also have an aligned slot, one being wider than the other. To snap together this hinge, it is required to pass the side arm or its tenon in the wider slot by a vertical by a vertical movement to insert it when this side arm is momentarily deflected to place it in an angular position external to its angular play between its open or closed position. In practice, this deflection is impractical for non-qualified personnel, and may also result in damage to the enveloping parts or decorative plates carried by the side arm.
Because of their large dimensions and difficulties in assembly, it is unreasonable to envisage that this type of snap-fit hinge could be combined with an elastic mechanism allowing a snap-effect between the open and closed positions, or an elastic displacement beyond the open position.
There are also known concealed joining hinges employing a ball and socket joint, i.e. a ball solid with the end of the side arm which is received in a spherical seat in a cavity in the front part's tenon. However, these hinges are inconvenient to assemble. Moreover, these hinges are also very difficult to manufacture and have reduced mechanical strength due to the fact that the solid connecting pin, which is at least as large as the hinge, is replaced by a small sphere. Premature wear of the seat risks leading to separation of the side arm from the frame.